flower – la flor
(Pronounced floor)
To remember that flower is pronounced floor (flor) in Spanish, use the following mnemonic:
The flower he tried to impress her with ended up on the floor (flor).

Flor is feminine, so it's la flor. Imagine that every flower is a lady:

Examples of flor (flower) in a sentence
La flor en el jardín es muy bonita.
(The flower in the garden is very pretty.)
Ella le regaló una flor roja a su madre.
(She gave her mother a red flower.)
El perfume huele a flor de naranja.
(The perfume smells like orange flower.)